Impedance simulator for simulating the impedance of an antenna radiating in an open space over a selected frequency band

ABSTRACT

An impedance simulator having the capability of simulating the operational impedance characteristics of a whip antenna in open field throughout a given frequency range. The simulator includes a cylindrical chamber of conductive, non-magnetic material coated on the interior surface with a lossy ferrite material. Coaxially mounted on the interior of the chamber is a coaxial conductor having at one end thereof a coaxial connector. The other end of the coaxial conductor has the center conductor thereof extending beyond the end of the outer conductor. This end of the inner conductor has mounted thereon a metallic disk lying in a plane perpendicular to the axis of the coaxial conductor. The utilization device, such as an r-f power source is attached to the coaxial connector. The assembly presents to the utilization device an impedance similar to that of a whip antenna in open field.

United States Patent Czerwinski IMPEDANCE SIMULATOR FOR SIMULATING THE IMPEDANCE OF AN ANTENNA RADIATING IN AN OPEN SPACE OVER A SELECTED FREQUENCY BAND 1 Sept. 16, 1975 Primary Examiner-Eli Lieberman Attorney, Agent, or FirmNathan Edelberg; Robert P. Gibson; Arthur L. Bowers 57] ABSTRACT An impedance simulator having the capability of simulating the operational impedance characteristics of a whip antenna in open field throughout a given frequency range. The simulator includes a cylindrical chamber of conductive, non-magnetic material coated on the interior surface with a lossy ferrite material. Coaxially mounted on the interior of the chamber is a coaxial conductor having at one end thereof a coaxial connector. The other end of the coaxial conductor has the center conductor thereof extending beyond the end of the outer conductor. This end of the inner conductor has mounted thereon a metallic disk lying in a plane perpendicular to the axis of the coaxial conductor. The utilization device, such as an r-f power source is attached to the coaxial connector. The assembly presents to the utilization device an impedance similar to that of a whip antenna in open field.

3 Claims, 2 Drawing Figures PATENTEU SEP 1 6 ms FIG. 1

FIG. 2

. 1 y IMPEDANCE SIMULATOR FOR SIMULATING THE IMPEDANCE or AN ANTENNA RADIATING IN AN OPEN SPACE OVER A SELECTED FRE UENCY I V This is a co'ntinuatio'n-i n-part of Application'Ser. No. 446,831, filed 24 Feb.1974, now abandoned.

BACKGROUND ,oF THE INVENTION l. Field of the Invention The present invention relates to an impedance simulator for use in indoor tuning, testing; and impedance matching of electronic equipment during the production and maintenance thereof. I

I 2. Description of the Prior Art In the field of electronic equipment .testing it has been the practice to use test equipment having lumped R, C, and L components as'dummy loads to simulate the operating impedance of whip antennas at specified frequenciesfSuch test equipmentusually included the use of a whip antenna placed in a chamber and connected at one end to a set of lumped R, C, and L ele ments. A discussion of such devices may be found in the August 1972 IEEE Transactions on Vehicular Technology, pp. 101-108. This approach is acceptable for narrow-band testing. However, in many applications, it is necessary to test devices which must operate over broad frequency bands. The wide-band frequency characteristics of lumped circuits can be expected to differ substantially from those of wide-band antennas thus necessitating many adjustments of the test equipment during the testing procedure. Moreover, experience has shown that dummy loads made up of tuned circuits require periodic adjustments when they must dissipate a substantial amount of power. Therefore, those concerned with the development of test equipment have long recognized the need for an impedance simulator capable of simulating the operational impedance characteristics of a ship antenna in open field over a broad band of frequencies. The present invention fulfills this need.

SUMMARY OF THE INVENTION The general purpose of this invention is to provide an impedance simulator capable of simulating the operational impedance characteristics of a whip antenna in open field over a broad band of frequencies and under relatively high power inputs. To attain this, the present invention contemplates a unique chamber having mounted therein a coaxial conductor with a conductive disk mounted thereon. The chamber is lined with a lossy ferrite material. A coaxial connector is provided at one end of the conductor for connecting the equipment being tested to the simulator. The combination of elements presents, to the equipment under test, an impedance substantially the same as that of a whip antenna in open field.

BRIEF DESCRIPTION OF THE DRAWINGS The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawing in which:

FIG. 1 shows a cut-away view of the preferred embodiment of the invention; and

FIG. 2 is a cross-section of the device taken on the line 2-2 of FIG. 1 looking in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the views, there is shown an impedance simulator 10 having a chamber 11 defined by a thinwalled cylindrical tube 12 and end plates 13 and 14. Tube 12 and plates 13 and 14 are made of a lightweight, non-magnetic conductive material such as aluminum. The interior surface of a tube 12 is coated with a relatively thick layer of lossy ferrite material 25. Plate 14 has a central aperture 17 through. which a cable from thedevice under test can be connected to the coaxial connector 19. Plate 14 is also removable so that testiequipment, e.g. an impedance matching device, may be actually placed inside the chamber ll.The coaxial eonneetor l9 feeds coaxial conductor 20 which has an outer conductor 21 and aninner conductor 22 spaced by a dielectric29. The inner conductor 22, being longer than the outer conductor 21, has an exposed portion 23whieh extends beyond one end of the outer conductor 21. Mounted at the'extreme end of portion 23 is a metal disk 24. A'p'air of dielectric spacers 26 and 27 maintain the coaxial conductor 20 in an axial relationship in tube 12. The impedance which the simulator 10 presents at the output of coaxial connector 19 is determined by the physical dimensions of and the types of materials used for the various elements. The value of the inductive and capacitive components of the impedance of the simulator 10 is predominantly a function of the length of the coaxial conductor 20 and the exposed portion 23, along with the size of the metal disk 24 plus its spacing from the metallic wall of tube 12. The necessary resistance is primarily a function of the size, amount and type of ferrite material 25.

In one such embodiment, which operated in the frequency band of 30 to 70 MHz, the simulator had the following dimensions:

inside diameter of the tube 12 12 inches;

length of tube 12 6 feet;

diameter of disk 24 9 inches;

distance from disk 24 to plate 13 8 inches;

thickness of disk 24 /2 inch;

length of exposed portion 23 1 Vs inches;

overall length of coaxial conductor 20 from its coaxial connector 19 to disk 24 52 inches;

The tube 12, plates 13 and 14, conductors 21 and 22, and the disk 24 were all made of highly conductive metals. The ferrite material 25 was of a type NZ-l made by Emerson and Cumming, Inc.

An impedance simulator having the specific parameters listed above was tested and compared with a prior art impedance simulator. During the test an impedance matching device was first connected to each of the devices, i.e. the present impedance simulator 10, and the whip antenna in open field, and the prior art impedance simulator. An rf power source was then connected to the impedance matching devices which in turn accepted watts from the power source. The voltage across the impedance matching devices was measured and recorded. The results of the test are listed as follows:

dance of a Whip antenna in open space over a selected frequency band comprising: Present Open Field Prior Art Freq Simulator Antenna Simuldmr a coaxial conductor having an outer conductor and (volts) (vol an inner conductor, said inner conductor having an 30 214 294 exposed portion extending beyond one end of said 42 459 349 239 a conductive disk mounted on the end of said ex- 23 posed portion of said inner conductor, said con- 56 188 230 99 1O ductive disk lying in a plane transverse to the axis of said coaxial conductor; and

70.5 102 I 100 24 a shield formed from a conductive material'spaced from and substantially surrounding said coaxial conductor and said conductive disk, a substantial area of the interior surface of said shield being coated with a ferrite material.

As can be seen from the test results, the present simulator 10 had an effect on the impedance matching device more like the effect of the open field whip antenna than did the prior art device.

Obviously many modifications and variations of the The device according to claim 1 and wherein Said present invention are possible in the light of the above Shield irfcludcs a cylindrical wall of non'magnetic mate teachings. it is therefore to be understood, that within havmg fi a Second Conducuve end P the scope of the appended claims, the invention may be The deviCC fl C r ing to l im 2 nd wher in Said practiced otherwise than is specifically described. conductive disk is perpendicular to the axis of said co- What is claimed is: v axial conductor. 1. An impedance simulatorvfor simulating the impe- 2S 

1. An impedance simulator for simulating the impedance of a whip antenna in open space over a selected frequency band comprising: a coaxial conductor having an outer conductor and an inner conductor, said inner conductor having an exposed portion extending beyond one end of said outer conductor; a conductive disk mounted on the end of said exposed portion of said inner conductor, said conductive disk lying in a plane transverse to the axis of said coaxial conductor; and a shield formed from a conductive material spaced from and substantially surrounding said coaxial conductor and said conductive disk, a substantial area of the interior surface of said shield being coated with a ferrite material.
 2. The device according to claim 1 and wherein said shield includes a cylindrical wall of non-magnetic material having first and second conductive end plates.
 3. The device according to claim 2 and wherein said conductive disk is perpendicular to the axis of said coaxial conductor. 